(a) Field
The following description relates to a fuel cell system.
(b) Description of the Related Art
Fuel cells are devices that electrochemically generate power by using fuel (hydrogen or reformed gas) and oxidant (oxygen or air) and directly convert the fuel (hydrogen or reformed gas) and oxidant (oxygen or air) supplied from the outside into electrical energy by an electrochemical reaction.
Pure oxygen or air containing a large amount of oxygen is used as the oxidant of the fuel cell and pure hydrogen or fuel containing a large amount of hydrogen, which is generated by reforming hydrocarbon-based fuel (LNG, LPG, CH3OH, etc.), is used as the fuel.
Hereinafter, a direct methanol fuel cell (DMFC) will be primarily described from among the fuel cells, for better comprehension and ease of description. The direct methanol fuel cell supplies high-concentration methanol to a fuel cell stack to generate electricity by reaction with the oxygen.
The direct methanol fuel cell uses high-concentration fuel to increase energy weight density. Water consumed in an anode is supplemented with water generated in a cathode in order to use the high-concentration fuel. In a known fuel cell system, fluids discharged from an outlet of the cathode are initially condensed by a heat exchanger in order to recover the water generated in the cathode. Thereafter, the condensed fluids and non-reacted fuel discharged from the anode are separated into a liquid and gas by a gas-liquid separator. The gas separated by the gas-liquid separator is discharged to the outside, and the liquid separated by the gas-liquid separator is mixed with the fuel and supplied back to the fuel cell stack.
In the known fuel cell system, condensed fluids and the non-reacted fuel are mixed with each other in the gas-liquid separator. The non-reacted fuel that flows into the gas-liquid separator has a comparatively higher temperature than the condensed fluids. As a result, some of the condensed fluids are vaporized when mixed with the non-reacted fuel.
When the condensed fluids are vaporized, water recovery efficiency is deteriorated, and a size of an apparatus condensing the fluids discharged from the cathode needs to be large so as to recover a proper amount of water.
In addition, when a temperature is high in an external environment, a temperature in the gas-liquid separator further increases, such that the water recovery efficiency is further deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.